The father of Stephen Lawrence dismissed an announcement by the Home Secretary that she will extend inquiries into allegations undercover officers were told to "smear" his family.

Neville Lawrence said that nothing short of a judge-led inquiry into the claims would be sufficient and that the fresh allegations had taken away the faith he had begun to build in the police.

From his home in Jamaica, a statement said he was "dismayed" over the new claims.

It said: "I've always felt that my family was under greater investigation than those guilty of killing my beloved Stephen.

"It is unthinkable that in the extremely dark days and months after my son's murder that my family were subject to such scrutiny.

Image Caption:Neville Lawrence, Stephen's father, is "dismayed" over new the allegations

"I am convinced that nothing short of a judge-led public inquiry will suffice and I have no confidence that the measures announced today will get to the bottom of this matter."

It comes after the Home Secretary told the House of Commons that Scotland Yard has asked the Independent Police Complaints Commission (IPCC) to supervise its handling of allegations that police tried to "smear" the Lawrence family.

Video:Lord Condon On Lawrence Smears

The claims emerged in an interview with a former undercover police officer, Peter Francis.

Theresa May MP said further allegations were likely to emerge before a report on alleged deliberate incompetence and corruption during the investigation into Stephen's murder.

She said: "They (Lawrence family) experienced an unspeakable tragedy, their pain was compounded by the many years in which justice was not done and these latest allegations still coming 20 years after Stephen's murder only add to their suffering.

"Given the nature of those allegations and the many years the Special Demonstration Squad was in existence, we should not be surprised if further allegations are made."

A report by Mark Ellison QC, commissioned by the Home Secretary last July, will investigate allegations of incompetence and corruption during the Lawrence investigation. It will now be delayed to incorporate the "smear" allegations.

Mr Francis said he was told to find "dirt" that could be used against members of the Lawrence family, shortly after the 18-year-old was killed in a racist attack in April 1993, The Guardian reported.

He was also asked to target the friend who witnessed the murder and campaigners angry at the failure to bring his killers to justice, the newspaper said.

Mr Lawrence's mother, Doreen, told the newspaper there was no justification for efforts to discredit her family for her son's murder.

The claims will be investigated by a team already looking into other possible abuses of responsibility carried out by undercover officers.

Derbyshire's Chief Constable Mick Creedon is heading the inquiry into claims officers assumed the identities of dead children and had inappropriate sexual relationships.

"Smearing the family of a murder victim would never be acceptable to me or my officers."

Lord Condon, who was Metropolitan Police commissioner at the time of Stephen's murder, said: "I'm not aware of any other senior officer in the Met at the time who would have authorised the sort of smear campaign that's been described."

The claims have surfaced as a result of a joint investigation into undercover policing by The Guardian and Channel 4's Dispatches programme, to be broadcast this evening.

Mr Francis, who reportedly posed as an anti-racist activist in the mid-1990s, said he came under "huge and constant pressure" to "hunt for disinformation" to undermine those arguing for a better investigation into the murder.

He told The Guardian: "I had to get any information on what was happening in the Stephen Lawrence campaign.

"They wanted the campaign to stop. It was felt it was going to turn into an elephant.

"Throughout my deployment there was almost constant pressure on me personally to find out anything I could that would discredit these campaigns."

Mr Lawrence, an aspiring architect, was stabbed to death by a group of up to six white youths in an unprovoked racist attack as he waited at a bus stop in Eltham, southeast London.

In January 2012, Gary Dobson and David Norris were found guilty of being involved in the attack and sentenced to life imprisonment after a forensic review of the case found significant new scientific evidence on clothing seized from their homes following the murder.

During the 19-year wait for justice by the family, there was a campaign by activists for more to be done to bring Stephen's killers to justice.

Responding to Mr Francis' claims, Mrs Lawrence told the Guardian: "Out of all the things I've found out over the years, this certainly has topped it."

Shadow home secretary Yvette Cooper described Mr Francis' claims as "shocking and appalling" and called for there to be a separate investigation into the "smear" claims.